Sheet feeding apparatus, sheet feeding method and control program

ABSTRACT

A sheet feeding apparatus provided with a fan for blowing air against sheets stacked on a sheet tray, a position detecting sensor for detecting the position of the sheets floated up by the fan, and a tray lifting and lowering mechanism for lifting and lowering the sheet tray. The tray lifting and lowering mechanism is controlled on the basis of a result of detection by the position detecting sensor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a sheet feeding apparatus for and a sheetfeeding method of feeding a sheet to a predetermined position, and acontrol program for executing a controlling method for the sheet feedingapparatus.

2. Related Background Art

An image forming apparatus such as a color copying machine or a colorprinter has heretofore been provided with a sheet feeding apparatus forfeeding a sheet cut into a predetermined size to a transferring positionin order to transfer a toner image formed on a photosensitive memberonto the sheet at the transferring position.

As the sheet feeding apparatus, besides one utilizing a frictionalroller, there is also, for example, one which air feeds sheets stackedon a stacking tray (see Japanese Patent Application Laid-Open No.S60-082537). According to this apparatus, for example, in order toeffect sheet feeding, air is blown against the uppermost portion of thesheets to thereby float up the sheets, and thereafter air suction iseffected to thereby suck the uppermost sheet and feed the sheet.

However, depending on the differences in sheet conditions such as thematerial of the surface of the sheet used, the basis weight of the sheetand the surface smoothness of the sheet, the magnitude of the closecontacting force between adjacent sheets in a sheet bundle differsgreatly. As this close contacting force between the sheets becomesgreater, there occurs a case where it becomes impossible to effect sheetseparation by the blowing of the air, and this has led to the problemthat the types of actually applicable sheets are restricted to a certainextent.

Such a problem is expected to be further actualized in the future, incolor copying machines and color printers as well as offset printingmachines, due to the new trend to use sheets of high smoothness such asart paper, coat paper and film to achieve a high quality of image.Particularly under a high-temperature and high-humidity environment,such sheets of high smoothness as mentioned above, because of being veryhigh in the close contacting force between sheets as compared with plainpaper, have the possibility that double feed may occur frequently orfeeding is not smoothly effected but wrong feeding may occur frequently.

In order to solve these problems, there are known techniques disclosed,for example, Japanese Patent Application Laid-Open No. H07-089625 andJapanese Patent Application Laid-Open No. H10-067442. In Japanese PatentApplication Laid-Open No. H07-089625, when air is to be blown againststacked sheets to thereby float the sheets, the uppermost sheet positionis detected and on the basis of the result of the position detection,the air discharge amount to be blown is adjusted to thereby control theposition of the floated-up sheets.

Also, in Japanese Patent Application Laid-Open No. H10-067442, when airis to be blown against stacked sheets to thereby float up the sheets,the uppermost sheet position is detected and an air nozzle dischargingthe air is moved to the detected position to thereby control theposition of the floated-up sheets.

However, to deter the state of the floated-up sheets within apredetermined range by the use of the aforedescribed technique of theair discharging force control (Japanese Patent Application Laid-Open No.H07-089625) or the air nozzle movement control (Japanese PatentApplication Laid-Open No. H10-067442), taking into account thedifferences in sheet conditions such as the material of the surface ofthe sheet used, the basis weight of the sheet and the smoothness of thesurface of the sheet, there become necessary a hard part which cancontrol an air discharging force or an air nozzle movement amount athigh resolving power.

For example, in a case where the rotating speed of a fan motor isminutely changed to thereby realize the control of the air dischargingforce, there becomes necessary an electric circuit for linearly changingthe rotating speed of the fan motor. Particularly, when a very widerange of air discharging force is required, there is the possibilitythat a plurality of fans conforming to the discharging force must bemounted and one of the plurality of fans must be selected on the basisof the sheet conditions to thereby minutely control the rotating speedof the fan motor.

Also, in a case where an air nozzle moving motor is added to therebyrealize the control of the air nozzle movement, there become necessary amechanical mechanism and a motor driving circuit necessary to move theair nozzle.

In a case where any of these techniques is used, it is impossible toavoid an increase in the cost of the apparatus itself, and this has ledto the problem that a sheet feeding apparatus of high performance cannotbe realized at a low cost.

SUMMARY OF THE INVENTION

In view of the above-noted problems peculiar to the conventional art,the present invention has as its object to provide a sheet feedingapparatus and a sheet feeding method of high performance and low costwhich can realize stable sheet feeding without being affected by thematerials of sheets, a control program and an image forming apparatusfor executing a controlling method for the sheet feeding apparatus.

In order to achieve the above object, the sheet feeding apparatus of thepresent invention for feeding sheets has:

a sheet tray on which the sheets are stacked;

a fan which blows air against the sheets so as to float up the sheetsstacked on the sheet tray;

a tray lifting and lowering mechanism which lifts and lowers thestacking tray; and

a position detecting sensor which detects the position of the sheetsfloated up by the fan;

the tray lifting and lowering mechanism being controlled so as to adjustthe position of the sheet tray on the basis of the result of detectionby the position detecting sensor.

Also, the sheet feeding method of the present invention successivelyexecutes:

an air discharging step of blowing air against sheets stacked on a sheettray on which the sheets are stacked to thereby float up the sheets;

a position detecting step of detecting the position of the sheetsfloated up by the air discharging step;

an adjusting step of adjusting the position of the sheet tray on thebasis of the result of detection by the position detecting step; and

a feeding step of feeding the sheets.

Also, the computer-readable control program of the present invention forexecuting a controlling method for a sheet feeding apparatus for feedingsheets, the sheet feeding apparatus having a sheet tray on which sheetsare stacked, a fan which blows air against the sheets so as to float upthe sheets stacked on the sheet tray, a tray lifting and loweringmechanism which lifts and lowers the sheet tray, and a positiondetecting sensor which detects the position of the sheets floated up bythe fan, and provided with an adjusting step of controlling the liftingand lowering operation of the tray lifting mechanism on the basis of theresult of detection by the position detecting sensor to thereby adjustthe position of the sheet tray.

Also, the image forming apparatus of the present invention has:

a sheet feeding apparatus for feeding sheets, having a sheet tray onwhich sheets are stacked, a fan which blows air against the sheets so asto float up the sheets stacked on the sheet tray, a tray lifting andlowering mechanism which lifts and lowers the sheet tray, and a positiondetecting sensor which detects the position of the sheets floated up bythe fan;

an image forming unit which forms images on the sheets fed by the sheetfeeding apparatus; and

a controller which controls the tray lifting and lowering mechanism soas to adjust the position of the sheet tray on the basis of the resultof detection by the position detecting sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing the construction of an imageforming apparatus on which is carried an air feeding unit according toan embodiment of the sheet feeding apparatus of the present invention.

FIG. 2 is a cross-sectional view showing the construction of a sheetdeck connected to an image forming apparatus main body shown in FIG. 1.

FIG. 3 is a block diagram showing the constructions of the image formingapparatus main body and the sheet deck.

FIG. 4 is a schematic view showing the construction of an operatingportion in the image forming apparatus according to the embodiment.

FIG. 5 is a cross-sectional view showing the construction of the airfeeding unit carried on the image forming apparatus according to theembodiment.

FIG. 6 is a flow chart showing the sheet feeding control of the airfeeding unit according to the embodiment.

FIG. 7 shows the relation between the sheet surface position of afloated-up sheet and a sheet feeding state.

FIG. 8 is a flow chart showing the sheet surface position control of theair feeding unit according to the embodiment.

FIG. 9 is a block diagram showing the internal construction of an imageprocessing portion according to the embodiment.

FIG. 10 is a block diagram showing the internal construction and theperipheral portion of an image memory portion according to theembodiment.

FIG. 11 is a block diagram showing the internal structure and theperipheral portion of an external I/F processing portion.

FIG. 12 shows the lower limits of a sheet detectable by a sheet float-uplower limit sensor and a sheet float-up upper limit sensor.

FIG. 13 is a cross-sectional view showing a modification of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the sheet feeding apparatus, the sheet feeding method andthe control program of the present invention will hereinafter bedescribed with reference to the drawings. The sheet feeding apparatusaccording to the present embodiment will be described as being appliedto an air feeding unit carried on an image forming apparatus such as,for example, a color copying machine or a color printer, but is notrestricted to such an apparatus. That is, it can be applied to all ofapparatuses for feeding a cut sheet to a predetermined position.

<Construction of the Image Forming Apparatus According to theEmbodiment>

FIG. 1 is a cross-sectional view showing the construction of an imageforming apparatus on which is carried an air feeding unit according toan embodiment of the sheet feeding apparatus of the present invention.

In FIG. 1, the reference numeral 100 designates an image formingapparatus main body. The reference numeral 101 denotes platen glass(original plate) as an original placing stand. The reference numeral 102designates a scanner comprised of an original illuminating lamp 103, ascanning mirror 104, etc. The image of an original placed on the platenglass 101 is scanned by the scanner 102 controlled so as to bereciprocally moved in predetermined directions (leftward and rightwarddirections as viewed in FIG. 1) by a motor (not shown). Reflected lightfrom the original is transmitted through a lens 108 via scanning mirrors104 to 106 and is imaged on an image sensor portion (CCD sensor) 109,whereby it is converted into an electrical signal.

The reference 120 denotes an exposure controlling portion comprised of alaser output portion and a polygon scanner or the like, and it applies alaser beam 129 to the photosensitive drum 110 of an image formingportion 126. The laser beam 129 is modulated on the basis of an imagesignal obtained as a result of predetermined image processing which willbe described later having been effected on an electrical signalresulting from photoelectrically converting the reflected light of theoriginal outputted from the image sensor portion 109.

As what constitute the image forming portion 126, a primary chargingdevice 112, a developing device 121, a transfer charging device 118, aseparation charging device 119, a cleaning apparatus 116 and apre-exposure lamp 114 are provided around the photosensitive drum 110.The photosensitive drum 110 is rotatively controlled in the directionindicated by the arrow as shown in FIG. 1 by a motor (not shown), and ischarged to desired potential by the primary charging device 112, andthereafter has the laser beam 129 applied thereto from an exposurecontrolling portion 120, whereby an electrostatic latent image is formedon the surface of the drum. The electrostatic latent image formed on thephotosensitive drum 110 is developed and visualized as a toner image bythe developing device 121.

On the other hand, a sheet fed from an upper cassette 131 or a lowercassette 132 is conveyed to the image forming apparatus main body 100 byconveying rollers 135 and 136, and passes through a main body conveyingpath 160, and thereafter is fed to a feed belt 130 by registrationrollers 137. Thereafter, the toner image visualized on thephotosensitive drum 110 is transferred to the sheet by the transfercharging device 118. On the photosensitive drum 110 after the transfer,any residual toner is removed by the cleaning apparatus 116, and anyresidual charges are eliminated by the pre-exposure lamp 114.

The sheet after the transfer is separated from the image forming portion126 by the separation charging device 119, and is conveyed leftwardly asviewed in FIG. 1 by the feed belt 130. The toner image on the sheet isre-charged by before-fixing charging devices 139 and 140, and ispressurized and heated in a fixing device 141, whereby it is fixed onthe sheet. The sheet thus subjected to fixing is discharged out of themain body 100 by sheet discharging rollers 142.

A sheet discharging flapper 154 changes over a sheet path on a sheetdischarging side and a sheet path on a two-side recording side or amultiplex recording side. The sheet discharged from the sheetdischarging rollers 142 is conveyed to the sheet path on the two-siderecording side or the multiplex recording side when the sheetdischarging flapper 154 is upwardly raised. In case of two-siderecording, the sheet subjected to the fixing on the first side thereofis discharged from the sheet discharging rollers 142, and is reversedthrough a reversing path 155, and is directed to a re-feeding tray 156through a lower conveying path 158.

A multiplex flapper 157 changes over a two-side recording sheet path anda multiplex recording sheet path. The multiplex flapper 157 is broughtdown in the left direction, whereby the sheet is directly directed tothe lower conveying path 158 without the intermediary of the reversingpath 155. By the sheet being directly directed to the lower conveyingpath 158 without the intermediary of the reversing path 155, multiplexrecording becomes possible. A feeding roller 159 feeds the sheet to theimage forming portion 126 side through a sheet path 160.

Discharge rollers 161 disposed near the sheet discharging flapper 154operates so as to discharge the sheet fed out from the sheet dischargingrollers 142 to the outside of the apparatus in a state in which thesheet discharging flapper 154 changed over to the discharging side (astate in which it is not upwardly raised). As previously described,during two-side recording (two-side copying) and multiplex recording(multiplex copying), the sheet discharging flapper 154 is upwardlyraised and the sheet subjected to fixing is stored in the re-feedingtray 156 through the lower conveying path 158.

The sheets stored in the re-feeding tray 156 are separated one by onefrom the lowermost sheet by the feeding roller 159, and the separatedsheet is again directed to the registration rollers 137 of the imageforming apparatus main body 100 through the sheet path 160.

When the sheet is to be discharged from the image forming apparatus mainbody 100 with its front and back sides reversed, the sheet dischargingflapper 154 is upwardly raised and the multiplex flapper 157 is broughtdown in the right direction. Thereby, the sheet to be discharged is oncefed to the reversing path 155 side, and at the timing whereat thetrailing edge of the sheet has passed a first feeding roller 162, thesheet is conveyed to a second feeding roller 162 a by a reversing roller163, and is discharged out of the apparatus by the discharge rollers161.

An automatic original conveying apparatus (DF) 180 separates only theuppermost sheet from an original bundle placed on an original placingstand 181 by a feeding roller 182, and conveys it onto the platen 101 byan original feeding roller 164. Thereafter, the original is scanned bythe scanner 102, and the scanned original is discharged onto an originaldischarging stand 183 or is again returned onto the original placingstand 181.

A discharged sheet treating apparatus 190 aligns and binds the sheetsdischarged from the image forming apparatus main body 100. When adischarged sheet bundle aftertreatment operation such as sorting orstapling is not set, the sheet passes through a conveying path 194 andis discharged onto a sheet discharging tray 191 without the intermediaryof a treatment tray 193. On the other hand, when the discharged sheetbundle aftertreatment operation is set, the sheets discharged one by onethrough a conveying path 195 are stacked and aligned on the treatmenttray 193. After the discharge of the sheet in the first sheet imageforming has been completed, the sheet bundle is stapled, and isdischarged in the form of a bundle to the sheet discharging tray 191 or192.

When the discharged sheet bundle aftertreatment operation is set,basically the sheets are bundle-discharged to the sheet discharging tray192, but depending on a condition such as the fully stacking state ofthe sheet discharging tray 192, control is effected so as to change overthe destination of discharge to the sheet discharging tray 191. Thesheet discharging trays 191 and 192 have their upward and downwardmovement controlled by a motor (not shown), and are moved so that beforethe start of the image forming operation, the tray stacking thedischarged sheets thereon may come to the position of the treatmenttray.

FIG. 2 is a cross-sectional view showing the construction of sheet decksconnected to the image forming apparatus main body 100 shown in FIG. 1.

A plurality of large-capacity sheet decks 1200 a to 1200 d are connectedin series to the image forming apparatus main body 100 shown in FIG. 1.Each of the sheet decks 1200 a to 1200 d is provided with a lifter 1201and a remaining amount detecting sensor (not shown) for detecting theremaining amount of sheets, and the lifter 1201 is adapted to be movedup in accordance with the amount of sheets so that the sheets may alwaysexist at a feeding position. Further, the sheet decks 1200 a to 1200 dhave a sheet conveying path, and feed the sheet sent from an upstreamside (the right side as viewed in FIG. 2) to a downstream side byconveying rollers 1203 and 1204.

Accordingly, in a system wherein the plurality of sheet decks 1200 a to1200 d are connected as in the present embodiment, the sheets fed by theupstream deck are successively conveyed therefrom through the conveyingpath of the downstream sheet deck, and are finally fed to the imageforming apparatus main body 100. The conveying path is designed to becapable of performing the conveying operation even when a sheetcontainer is brought into an open state in order to supply the sheets.Also, design is made such that sheet information such as the sheet size,sheet type and basis weight of the sheets to be stored in the respectivesheet decks 1200 a to 1200 d can be set from an operating portion (notshown).

The upper cassette 131 and lower cassette 132 in the image formingapparatus main body 100 and further, the sheet decks 1200 a to 1200 d,are provided with an air feeding unit (sheet feeding apparatus) forminga feature of the present embodiment which will be described later indetail with reference to FIGS. 5 to 8, and the sheets reliably separatedone by one by this air feeding unit are successively conveyed to theimage forming portion 126 by the conveying rollers 135 or 136, orconveying rollers 1203 and 1204.

FIG. 3 is a block diagram showing the constructions of a controllingportion 100A in the image forming apparatus main body 100 shown in FIG.1, and the controlling portion 1200A of the sheet decks shown in FIG. 2.

The controlling portion 100A in the image forming apparatus main body100 is comprised of a CPU 201, a ROM 206, a RAM 205, a communicationinterface (I/F) 207, an input-output port 204, an operating portion 203,an image processing portion 170 and an image memory portion 3.

The CPU 201 effects the basic control of the image forming apparatusmain body 100, and the ROM 206 into which a control program is written,the work RAM 205 for effecting processing, and the input-output port 204are connected to an address bus by a data bus. Some area of the RAM 205is a backup RAM from which data is not erased even if a power supply isswitched off. The input-output port 204 has connected thereto variousload devices such as a motor and a clutch controlled by the imageforming apparatus main body 100, and an input device such as a sensorfor detecting the position of the sheet.

The CPU 201 sequentially effects the control of an input and an outputthrough the input-output port 204 in accordance with the contents of thecontrol program stored in the ROM 206, and executes an image formingprocess. Also, the CPU 201 has the operating portion 203 connectedthereto, and controls the displaying portion and the key inputtingportion of the operating portion 203. A user instructs the CPU 201 tochange over an image forming operation mode and display through the keyinputting portion of the operating portion 203, and the CPU 201 effectsthe display of the operating state of the image forming apparatus mainbody 100 and the operation mode set by a key input, to the displayingportion of the operating portion 203. Further, the CPU 201 has connectedthereto the image processing portion 170 for processing a signalconverted into an electrical signal by the image sensor portion 109, andthe image memory portion 3 for accumulating processed images therein.

The controlling portion 1200A of the sheet deck 1200 is comprised of aCPU 2201, a ROM 2202, a RAM 2203, a communication interface (I/F) 2204,an input-output port 2205 and an operating portion 2206 in order torealize the operation described with reference to FIG. 2. The CPU 2201inputs the results of detection thereto from an upper limit sensor 608and a lower limit sensor 607 which will be described later, through theinput-output port 2205, and outputs a driving command to a tray liftingand lowering motor 604, a loosening fan 609 and a feed fan 612 whichwill be described later.

FIG. 4 is a schematic view showing the construction of the operatingportion 203 in the image forming apparatus according to the presentembodiment.

In FIG. 4, the reference numeral 3001 designates a displaying portion onwhich are displayed various messages such as the operating state of theapparatus and work instructions to the user, and a work procedure or thelike. Also, the surface of the displaying portion 3001 is constituted bya touch panel, and by being touched, it works as a selecting key. Thereference numeral 3002 denotes ten keys for inputting numerals. Thereference numeral 3003 designates a start key, and by depressing thiskey, a copying operation is started.

<Construction of the Air Feeding Unit>

Description will now be made of the construction of an air feeding unitforming a feature of the present embodiment.

FIG. 5 is a cross-sectional view showing the constructions of the airfeeding unit carried on the above-described image forming apparatus andthe peripheral portion of the cassette 132.

The air feeding unit according to the present embodiment is provided notonly in the cassette 132, but also in the cassette 131 in theabove-described image forming apparatus main body 100 and thelarge-capacity sheet decks 1200 a to 1200 d. Here, the air feeding unitprovided in the cassette 132 will be described as an example.

In FIG. 5, a cassette floor plate 602 as a sheet tray for stackingsheets thereon is provided in the interior of the cassette 132. Thecassette floor plate 602 is movable up and down by the driving of a traylifting and lowering motor 604 via a pulley 603. By the cassette floorplate 602 being lifted and lowered, a sheet bundle stacked on thecassette floor plate 602 is moved up and down.

An encoder is mounted on the tray lifting and lowering motor 604, and itis possible to know the driving amount of the tray lifting and loweringmotor 604, i.e., the amount of vertical movement of the cassette floorplate 602, by this encoder. A tray lower limit detecting sensor 605 isprovided to detect the lower limit position of the cassette floor plate602.

On the other hand, above the air feeding unit, there are disposed asheet presence or absence detecting sensor 606 for detecting the heightof the sheets, a sheet float-up lower limit sensor 607 and a sheetfloat-up upper limit sensor 608. The sheet presence or absence detectingsensor 606 detects the sheets by a flag sensor. The sheet float-up lowerlimit sensor 607 and the sheet float-up upper limit sensor 608 detectthe sheets by optical type sensors.

The sheet presence or absence detecting sensor 606 is disposed below thesheet float-up lower limit sensor 607 and the sheet float-up upper limitsensor 608, and design is made such that when a sheet bundle 601 stackedon the cassette floor plate 602 comes up to a feeding start position,the sheet presence or absence detecting sensor 606 can detect the uppersurface of the sheet bundle 601 earlier than the sheet float-up lowerlimit sensor 607 and the sheet float-up upper limit sensor 608.

Also, the sheet float-up lower limit sensor 607 and the sheet float-upupper limit sensor 608 are sensors for detecting the position of thesheets floated up by wind pressure by the loosening fan 609 which willbe described later. The sheet float-up lower limit sensor 607 issensitivity-adjusted so as to be capable of detecting the floated-upsheet located below the sheet float-up upper limit sensor 608.Consequently, design is made such that whether the floated-up sheets arelocated within a predetermined range can be detected by the use of thesheet float-up lower limit sensor 607 and the sheet float-up upper limitsensor 608. The relation between the detecting state of the sheetfloat-up lower limit sensor 607 and the sheet float-up upper limitsensor 608 and the sheet feeding state will be described later.

Further, the loosening fan 609 and a loosening fan duct 610 areinstalled for the purpose of loosening the sheet bundle 601 contained inthe cassette 132 prior to the feeding operation. Wind pressure in adischarging direction produced by the loosening fan 609 being rotated isgiven to the neighborhood of the uppermost sheet of the sheet bundle 601by the loosening fan duct 610, whereby a plurality of sheets areprevented from being fed at a time (=double feed) during the sheetfeeding operation.

Also, a feed belt 611, a feed fan 612 and a feed fan duct 613 areinstalled as a sheet feeding mechanism. Wind pressure in a suckingdirection produced by the feed fan 612 being rotated is given to thefeed belt 611 through the feed fan duct 613. The uppermost sheet of thesheet bundle 601 is sucked onto the feed belt 611 by the wind pressuregiven to the feed belt 611. The sheet sucked onto the feed belt 611 isconveyed to a feeding retry sensor 620 and a pulling-out roller 136 sideby the feed belt 611 being rotated in a direction indicated in FIG. 5.

FIG. 5 shows a state in which the sheet has been sucked by the feed fan612, but when the sheet float-up lower limit sensor 607 and the sheetfloat-up upper limit sensor 608 are to detect the floated-up position ofthe sheets, as shown in FIG. 12, during the time when the feed fan 612is not operated, but the loosening fan 609 is operated, the upward anddownward movement of the cassette floor plate 602 is controlled on thebasis of the sheet float-up lower limit sensor 607 and the sheetfloat-up upper limit sensor 608, as will be described later.

The lower limits of the sheet detectable by the sheet float-up lowerlimit sensor 607 and the sheet float-up upper limit sensor 608 are asshown in FIG. 12. In FIGS. 5 and 12, the sheet float-up lower limitsensor 607 and the sheet float-up upper limit sensor 608 are arranged ina sheet feeding direction, but may be arranged in a directionperpendicular to the sheet feeding direction, whereby more accuratedetection becomes possible.

<Sheet Feeding Control of the Air Feeding Unit>

Description will now be made of the sheet feeding control of the airfeeding unit of the above-described construction.

FIG. 6 is a flow chart showing the sheet feeding control of the airfeeding unit according to the present embodiment. A program according tothe flow chart of FIG. 6 is stored in the ROM 2202 in the controllingportion 1200A and is executed, whereby it is possible to realize thefollowing controlling method. The program according to the flow chart ofFIG. 6 is stored in the ROM 206 in the controlling portion 100A of theimage forming apparatus main body 100 and is executed, whereby it isalso possible to realize the following controlling method.

First, when at a step S701, instructions to start feeding are received,whether the sheet is the first sheet to be subjected to the feedingoperation is determined at the next step S702. If at the step S702, itis the first sheet, at a step S703, the rotation of the loosening fan609 is started in order to float up the uppermost sheet and subsequentseveral sheets of the sheet bundle 601, and at a step S704, the feed fan612 is rotated to cause the sheets to be sucked onto the feed belt 611.

Next, at a step S705, waiting is effected for longer one of the timefrom the start of the rotation of the loosening fan 609 until theuppermost sheet is floated up and it becomes possible to sufficientlyloosen the sheets, and the time until the feed fan reaches wind pressuresufficient to cause the sheets to be sucked, and then, at a step S706,the feed fan duct 613 is brought into an open state in order to causethe upper sheet to be sucked onto the feed belt 611.

Thereafter, at a step S707, waiting is effected until a sheet suckingsensor (not shown) detects that the sheet has been sucked onto the feedbelt 611, and at a point of time whereat the sucking of the sheet couldbe detected, at a step S708, the feed belt 611 is rotated to therebystart the sheet feeding to the image forming portion 170.

On the other hand, if at the step S702, the sheet is not the firstsheet, the processing of the step S703 to the step S705 is not carriedout, but at predetermined timing, the feeding of the sheets is effectedby only the processing of the step S706 and subsequent steps.

<Relation Between the Sheet Surface Position of the Floated-up Sheet andthe Sheet Feeding State>

FIG. 7 shows the relation between the sheet surface position of thefloated-up sheet and the sheet feeding state.

Reference is now had to this FIG. 7 to describe below the sheet surfaceposition of the uppermost sheet floated by the loosening fan 609 isrelated to the sheet feeding state.

In a state 800, both of the sheet float-up lower limit sensor 607 andthe sheet float-up upper limit sensor 608 have detected the sheet. Thatis, this is a state in which the sheet surface of the floated-upuppermost sheet has come too close to the feed belt 611, and is a statein appropriate to sheet feeding in which the sheets floated up beneaththe uppermost sheet may be highly liable to be also sucked together tothereby cause double feed.

A state 803, like the state 800, is a state in which the sheet float-upupper limit sensor 608 has detected the sheet surface, but the sheetfloat-up lower limit sensor 607 has not detected the sheet surface, andthis is a state in which one of the sensors 607 and 608 is highlyprobably abnormal and normal control cannot be expected. In the presentembodiment, design is made such that when this state occurs, the user,the operator or a serviceman is notified of the trouble of the airfeeding unit and if the air feeding unit is in operation, it is stoppedand the sheet feeding from the cassette and the sheet deck which are inan abnormal state is inhibited.

A state 802 is a state in which neither of the sheet float-up lowerlimit sensor 607 and the sheet float-up upper limit sensor 608 has notdetected the sheet, that is, the sheet surface of the floated-upuppermost sheet is too far from the feed belt 611, and is a stateinappropriate to sheet feeding in which the uppermost sheet cannot besucked onto the feed belt 611 to thereby cause faulty feeding with ahigh possibility.

A state 801 is a state in which the sheet float-up lower limit sensor607 has detected the sheet and the sheet float-up upper limit sensor 608has not detected the sheet, and is a state appropriate to sheet feedingin which such problems as double feed and faulty sheet feeding may notarise.

<Sheet Surface Position Control>

Reference is now had to the flow chart of FIG. 8 to describe the sheetsurface position control of the uppermost sheet for locating the sheetsurface of the floated-up uppermost sheet in the above-describedappropriate state 801.

FIG. 8 is a flow chart showing the sheet surface position control of theair feeding unit according to the present embodiment, and this sheetsurface position control is executed during the aforedescribed sheetfeeding control of FIG. 6. A program according to the flow chart of FIG.8 is stored in the ROM 206 in the controlling portion 100A and isexecuted, whereby it becomes possible to realize the followingcontrolling method.

First, at a step S900, whether the feeding operation has been started isdetermined, and when the feeding operation is started, at a step S901,the operation of initializing the sheet surface is performed before theloosening fan 609 is rotated and the uppermost sheet is floated up. Inthe present embodiment, the sheet surface initializing position is abovethe sheet presence or absence detecting sensor 606, and near the sheetfloat-up lower limit sensor 607 with the difference in the setting ofthe wind pressure of the loosening fan 609 resulting from the differencein the materials of the sheets taken into account.

At the next step S902, whether the loosening fan 609 has reached apredetermined rotating speed is determined. That is, design is made suchthat waiting is effected until there is brought about a state in whichwind pressure optimum for floating up the sheet is produced, thereafterthe sheet surface position control of a step S903 and subsequent stepsis started.

At the step S903, whether the sheet float-up lower limit sensor 607 hasdetected the sheet surface is first determined. If the sensor 607 hasnot detected the sheet surface, at a step S905, the tray lifting andlowering motor 604 is driven to lift the cassette floor plate 602 by apredetermined distance, thereafter at a step S908, the sheet feedpossible flag is cleared to thereby stop the sheet feeding operation.

On the other hand, if at the step S903, the sensor 607 has detected thesheet surface, whether the sheet float-up upper limit sensor 608 hasdetected the sheet surface is determined at a step S904. If at the stepS904, the sensor 608 has not detected the sheet surface, it is judgedthat this is a state appropriate to the sheet feeding operation, and ata step S907, the sheet feed possible flag is set to thereby start thesheet feeding operation (for example, when the sheet feed possible flagis set, the feed fan duct 613 becomes open at the step S706 of FIG. 6),and at a step S909, the next detection timing by the sheet float-uplower limit sensor 607 and the sheet float-up upper limit sensor 608 iswaited for.

On the other hand, if at the step S904, the sensor 608 has detected thesheet surface, at a step 906, the tray lifting and lowering motor 604 isdriven to lower the cassette floor plate 602 by a predetermineddistance, and at a step S908, the sheet feed possible flag is cleared tothereby stop the sheet feeding operation.

After the processing of the step S908 when the sheet float-up lowerlimit sensor 607 has not detected the sheet surface, or when the sheetfloat-up upper limit sensor 608 has detected the sheet surface, the stepS909 of waiting until the next detection timing is executed. Here, thewaiting time at the step S909 is judged by the sheet feed possible flag,and is controlled so as to be a relatively short time to detect anychange in the sheet surface position with high resolving power duringthe sheet feeding operation in which the same flag is set, and to be atime which can satisfy both of the time until the sheet surface is movedby a predetermined distance and the time until the floated-up positionof the sheet becomes stable by the sheet surface having been changed,during the stoppage of the sheet feeding operation in which the sameflag is cleared.

Then, at a step S910, the completion of the feeding operation isdetermined, and if the feeding operation should be continued, return ismade to the step S903, where the sheet surface position control isrepeated, and if the feeding operation has been completed, return ismade to the step S900, where the start of the next feeding operation iswaited for.

Only the sheet float-up lower limit sensor may be provided to therebycontrol the tray lifting and lowering motor 604 so as to lift thecassette floor plate 602 by a predetermined amount on the basis of achange from a state in which the sheet float-up lower limit sensordetects the sheet to a state in which the same sensor does not detectsthe sheet. However, the float-up amount of the sheet floated up by theloosening fan 609 is various depending on the material of the sheet, thehumidity absorbing state of the sheet resulting form room temperatureand humidity, etc. Accordingly, it is difficult to appropriatelyestimate the float-up amount of the sheet. Consequently, in such aconstruction, it is feared that for example, double feed may occur dueto the float-up amount being too great when the cassette floor plate 602is lifted by a predetermined amount.

In a case where as in the above-described present embodiment, on thebasis of the result of the detection by the two sensors, i.e., the sheetfloat-up lower limit sensor 607 and the sheet float-up upper limitsensor 608, control is effected so as to lower the cassette floor plate602 if the position of the sheet is higher than an upper limit position,and to lift the cassette floor plate 602 if the position of the sheet islower than a lower limit position, whereby in a case where the sheet islocated within a range in which feeding is effected appropriately, ascompared with a case where a single sensor is used, it becomes possibleto effect the feeding of the sheets more stably.

While in the present embodiment, description has been made of thecontrol of locating the sheet surface of the uppermost sheet floated upby the loosening fan 609 within a predetermined range by using the sheetfloat-up lower limit sensor 607 and the sheet float-up upper limitsensor 608 as position detecting sensors, a distance measuring sensor Kdisposed on the feed belt 611 for measuring the distance from the feedbelt 611 to the sheet surface of the sheet located below the feed belt611 may be used as a position detecting sensor (see FIG. 13). Bymeasuring the distance from the feed belt 611 to the sheet surface ofthe floated-up uppermost sheet by the distance measuring sensor K, it ispossible to control the distance from the feed belt 611 so as to belocated within a predetermined range, and even by such a construction,it is possible to obtain an effect similar to that of theabove-described embodiment.

Thus, in the present embodiment, the sheet feeding operation can beperformed with the sheet floated up to an appropriate position at whichit can be sucked onto the feed belt 611, and therefore very stable sheetfeeding such as reliable single sheet feeding can be realized at a lowcost without being affected to the material or the like of the sheet.

<Processing by the Image Processing Portion 170, the Image MemoryPortion 3 and the External I/F Processing Portion 4>

The processing by the image processing portion 170, the image memoryportion 3 and the external I/F processing portion 4 will hereinafter bedescribed with reference to FIGS. 9, 10 and 11.

FIG. 9 is a block diagram showing the internal construction of the imageprocessing portion 170.

First, describing the flow of processing when a scanned image isprinted, an original image imaged on the CCD sensor 109 through the lens108 is converted into an analog electrical signal by the CCD sensor 109.The converted image information is inputted to an analog signalprocessing portion 300, and is subjected to sampling and holding, thecorrection of a dark level, etc., and thereafter isanalog/digital-converted (A/D-converted) by an A/D•SH processing portion301, and further, shading correction is effected on the digitizedsignal. In the shading correction, correction for the unevenness of eachpixel the CCD sensor 109 has, and correction for the unevenness of thequantity of light based on the light distributing characteristic of theoriginal illuminating lamp 103 are effected.

Thereafter, in an RGB inter-line correcting portion 302, correctionamong R(red), G(green) and B(blue) lines is effected. Light inputted toeach of the R, G and B light receiving portions of the CCD sensor 109 ata certain point of time deviates on the original in accordance with thepositional relation of the respective R, G and B light receivingportions and therefore, synchronism is taken here among the R, G and Bsignals.

Subsequently, an input masking process is carried out in an inputmasking portion 303, and conversion from luminance data into densitydata is effected. That is, the RGB value as it has been outputted fromthe CCD sensor 109 is affected by a color filter mounted on the CCDsensor 109 and therefore, the influence thereof is corrected and theaforementioned RGB value is converted into a genuine RGB value.Thereafter, the image data is zooming-processed at a desired zoomingrate in a zooming portion 304, and the zooming-processed image data issent to and accumulated in the image memory portion 3. Image data from acomputer 11 shown in FIG. 11 is also inputted to the image memoryportion 3 through an external I/F processing portion 4.

When the accumulated images are to be printed, the image data is firstsent from the image memory portion 3 to a γ-correcting portion 305. Inthe γ-correcting portion 305, in order to provide output datacorresponding to a density value set by the operating portion 203,original density data is converted into density data corresponding todesired output density on the basis of a look-up table (LUT) taking thecharacteristic of the printer into account.

Thereafter, the density data is sent to a binarizing portion 306. In thebinarizing portion 306, the binarization of multi-value density data iseffected. In the case of multi-value density data, e.g. density data of8 bits, the density value assumes a value between “0” to “255”, but bybeing binarized, the density value becomes, for example, “0” or “255”.That is, in order to represent the density of a certain pixel, data of 8bits was necessary, whereas by being binarized, a data amount of 1 bitbecomes enough. Thereby, a memory capacity for storing the image data isreduced. On the other hand, however, the gradation of the image changesfrom the original 256 gradations to 2 gradations and therefore, in thecase of image data including many halftones such as a photographicimage, it is said that the quality of image thereof is generallyremarkably deteriorated by the binarization of the image.

So, pseudo halftone expression by binarized data becomes important.Here, an error diffusing method is used as a technique of effectinghalftone expression in a pseudo fashion by binary data. In this method,when the density of a certain image is greater than a certain thresholdvalue, it is regarded as density data of “255”, and when it is equal toor less than a certain threshold value, it is regarded as density dataof “0” and is binarized, thereafter the difference between actualdensity data and the binarized density data is obtained as an errorsignal, and is distributed to peripheral pixels. The distribution of theerror is effected by multiplying the error resulting from thebinarization by a weight coefficient on a predetermined matrix, andadding the result to the peripheral pixels. Thereby, the average densityvalue of the entire image is preserved, and the halftone can beexpressed in a pseudo fashion by binary.

The binarized density data is sent to a smoothing portion 307 in theprinter portion 2. In the smoothing portion 307, the complementing ofthe data is effected so that the end portions of the line of thebinarized image may become smooth, and the image data subjected to thecomplementing is outputted to the exposure controlling portion 120. Theexposure controlling portion 120, as previously described, forms theelectrostatic image of the image data on the photosensitive drum 110.

Description will now be described of the flow of the processing when thescanned image data is forwarded via a network.

The first half portion of the description in which the density data isaccumulated in the image memory portion 3 is the same as the flow of theprocessing during the aforedescribed print, thereafter the image data issent form the image memory portion 3 to the external I/F processingportion 4, from which the image data is forwarded to a desired computervia the network.

FIG. 10 is a block diagram showing the interval construction andperipheral portion of the image memory portion 3.

The image memory portion 3 is comprised of a page memory 401, a memorycontroller portion 402, a compressing/decompressing portion 403 and ahard disk 404.

The image data sent from the external I/F processing portion 4 and theimage processing portion 170 to the image memory portion 3 is writteninto the page memory 401 by the memory controller portion 402, andthereafter is sent to the printer portion 2 through the image processingportion 170, or is accumulated in the hard disk 404. When the image datais to be accumulated in the hard disk 404, the image data isdata-compressed in the compressing/decompressing portion 403, and iswritten into the hard disk 404 as compressed data.

Also, the memory controller portion 402 effects the reading-out of theimage data stored in the hard disk 404 to the page memory 401. At thattime, the compressed data read out from the hard disk 404 isdecompressed through the compressing/decompressing portion 403, and theimage data restored to the original state is written into the pagememory 401. Further, the memory controller portion 402 effects thegeneration of a DRAM refreshing signal to be sent to the page memory401. It also effects the mediation of the access from the external I/Fprocessing portion 4, the image processing portion 170 and the hard disk404 to the page memory 401. It further effects the determination controlof a writing address to the page memory 401, a reading-out address fromthe page memory 401, and a reading-out direction or the like inaccordance with the instructions of the CPU 201. By these processes, theCPU 201 arranges a plurality of original images and effects lay out inthe page memory 401 and moreover, becomes capable of controlling thefunction of outputting them to the printer portion 2 through the imageprocessing portion 140, the function of cutting out and outputting onlya part of the images, and the function of effecting the rotation of theimages.

Also, for example, regarding a sorting mode, the control of reading outand printing images in the order in which they have been recorded in theimage memory portion 3 is repeated a plurality of times and executed ona certain original bundle. By such control being effected, even in afinisher having only a few bins like the discharged sheet processingapparatus 190 in the present embodiment, the same role as that of asorter having a number of bins can be played.

FIG. 11 is a block diagram showing the internal structure and peripheralportion of the external I/F processing portion 4.

The external I/F processing portion 4 introduces image data from thereader portion 1 thereinto through the image memory portion 3, and sendsthe image data to an external computer or an external facsimileapparatus through a network or a phone line. Also, it outputs image datasend thereto from the external computer or the external facsimileapparatus through the phone line to the printer portion 2 through theimage memory portion 3 and the image processing portion 170 to therebyeffect image forming.

The external I/F processing portion 4 is comprised of a core portion506, a facsimile portion 501, a hard disk 502 for preserving thecommunication image data of the facsimile portion 501 therein, acomputer interface portion 503 connected to an external computer 11, aformatter portion 504 and an image memory portion 505.

The facsimile portion 501 is connected to a public phone line through amodem (not shown), and effects the reception of facsimile communicationdata from the public phone line and the transmission of facsimilecommunication data to the public phone line. In the facsimile portion501, the facsimile function of effecting facsimile transmission at adesignated time, or transmitting image data in response to an inquiry bya designated password from a partner is realized by the utilization ofan image for facsimile preserved in the hard disk 502. Thereby, after animage has once been sent from the reader portion 1 to the facsimileportion 501 through the image memory portion 3 and the image has beenpreserved in the hard disk 502 for facsimile, facsimile transmission canbe effected without the reader portion 1 and the image memory portion 3being used for the facsimile function.

The computer interface portion 503 is an interface portion which effectsdata communication with the external computer 11, and has a local areanetwork (LAN), a serial I/F, an SCSI-I/F, a centro I/F for inputting thedata of the printer, etc. Through this computer interface portion 503,the states of the printer portion 2 and the reader portion 1 arecommunicated to the external computer 11. Or by the instructions fromthe external computer 11, the forwarding of an image read by the readerportion 1 to the external computer 11 is effected.

The computer interface portion 503 also receives print image data fromthe external computer 11. At that time, the print image datacommunicated from the external computer 11 is described in an exclusiveprinter code and therefore, in the formatter portion 504, thecommunicated data code is converted into raster image data which caneffect image forming in the printer portion 2. The converted rasterimage data is evolved to the image memory portion 505 by the formatterportion 504.

On the other hand, when the image data is to be transmitted to theexternal computer 11 through the computer interface portion 503, theimage formatter 504 effects the conversion of the print image data sentthereto from the image memory portion 3 into an image formatrecognizable by the external computer 11, in the image memory portion505.

The image memory portion 505 is used as a memory which evolves theraster image data of the formatter portion 504, as described above, andbesides, is also used when the image data from the reader portion 1 issent to the external computer 11 (network scanner function). That is,when the image from the reader portion 1 is to be sent to the externalcomputer 11 via the computer interface portion 503, the image data sentfrom the image memory portion 3 is once evolved to the image memoryportion 505, where it is converted into the form of data to be sent tothe external computer 11, and then is transmitted from the computerinterface portion 503 to the external computer 11.

The core portion 506 controls and manages data forwarding mutuallyeffected among the facsimile portion 501, the computer interface portion503, the formatter portion 504, the image memory portion 505 and theimage memory portion 3. Thereby, even if a plurality of image outputportions are connected to the external I/F processing portion 4, andeven if the image forwarding path to the image memory portion 3 issingle, exclusive control and degree-of-priority control are effectedunder the management by the core portion 506 and therefore, imageoutputting is effected appropriately.

The present invention is not restricted to the apparatus of theabove-described embodiment, but may be applied to a system comprised ofa plurality of apparatuses, or may be applied to an apparatus comprisinga single device. Of course, the present invention is also completed bysupplying a system or an apparatus with a storage medium storing thereinthe program code of software for realizing the function of theaforedescribed embodiment, and the computer (or CPU or MPU) of thesystem or the apparatus reading out and executing the program codestored in the storage medium.

In this code, the program code itself read out form the storage mediumrealizes the function of the aforedescribed embodiment and thus, thestorage medium storing the program code therein constitutes the presentinvention. As the storage medium for supplying the program code, use canbe made, for example, of a Floppy (registered trademark) disk, a harddisk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, amagnetic tape, a non-volatile memory card or a ROM. Also, of course, bythe program code read out by the computer being executed, not only thefunction of the aforedescribed embodiment is realized, but also there iscovered a case where on the basis of the instructions of the programcode, an OS or the like working on the computer effects part or thewhole of actual processing, and by the processing, the function of theaforedescribed embodiment is realized.

Further, of course, there is also covered a case where the program coderead out from the storage medium is written into a memory provided in afunction enlarging board inserted in a computer or a function enlargingunit connected to a computer, thereafter on the basis of theinstructions of the next program code, a CPU or the like provided in theenlarging board or the enlarging unit performs the enlarging function tothereby effect part or the whole of actual processing, and by theprocessing, the function of the aforedescribed embodiment is realized.

This application claims priority from Japanese Patent Application No.2004-083349 filed on Mar. 22, 2004, which is hereby incorporated byreference herein.

1-13. (canceled)
 14. A sheet feeding apparatus, comprising: a tray onwhich sheets are stacked; an air discharging portion configured to blowair against the sheets on said tray to float up a sheet; a sheet feederconfigured to feed the sheet floated up by said air discharging portion;a tray lifting and lowering portion configured to lift and lower saidtray in a horizontal attitude; a position detecting unit configured todetect a position of an uppermost sheet which is being floated up bysaid air discharging portion; and a controlling portion adapted to letsaid tray lifting and lowering portion lower said tray when theuppermost sheet being floated up is above an upper limit of apredetermined range, and let said tray lifting and lowering portion liftsaid tray when the uppermost sheet being floated up is below a lowerlimit of said predetermined range, so that a floating position of theuppermost sheet falls within said predetermined range based on adetection result of said position detecting unit.
 15. A sheet feedingapparatus according to claim 14, wherein said position detecting unitcomprises: a first sensor configured to detect a position of theuppermost sheet being floated up above the upper limit of saidpredetermined range; and a second sensor configured to detect a positionof the uppermost sheet being floated up above the lower limit of saidpredetermined range.
 16. A sheet feeding apparatus according to claim14, wherein said sheet feeder comprises a belt which sucks the sheet bya lower surface of said belt to convey the sheet.
 17. A sheet feedingapparatus according to claim 16, wherein said position detecting unitcomprises a distance measuring sensor configured to measure a distancefrom said lower surface of said belt to the uppermost sheet which isbeing floated up by said air discharging portion.
 18. A sheet feedingapparatus according to claim 14, wherein said controlling portion doesnot let said tray lifting and lowering portion lift and lower said traywhen the uppermost sheet is within said predetermined range.
 19. Animage forming apparatus, comprising: a tray on which sheets are stacked;an air discharging portion configured to blow air against the sheets onsaid tray to float up a sheet; a sheet feeder configured to feed thesheet floated up by said air discharging portion; an image formingportion configured to form an image on the sheet fed by said sheetfeeder; a tray lifting and lowering portion configured to lift and lowersaid tray in a horizontal attitude; a position detecting unit configuredto detect a position of an uppermost sheet which is being floated up bysaid air discharging portion; and a controlling portion adapted to letsaid tray lifting and lowering portion lower said tray when theuppermost sheet being floated up is above an upper limit of apredetermined range, and let said tray lifting and lowering portion liftsaid tray when the uppermost sheet being floated up is below a lowerlimit of said predetermined range, so that a floating position of theuppermost sheet falls within said predetermined range based on adetection result of said position detecting unit.
 20. An image formingapparatus according to claim 19, wherein said position detecting unitcomprises: a first sensor configured to detect a position of theuppermost sheet being floated up above the upper limit of saidpredetermined range; and a second sensor configured to detect a positionof the uppermost sheet being floated up above the lower limit of saidpredetermined range.
 21. An image forming apparatus according to claim19, wherein said sheet feeder comprises a belt which sucks the sheet bya lower surface of said belt to convey the sheet.
 22. An image formingapparatus according to claim 21, wherein said position detecting unitcomprises a distance measuring sensor configured to measure a distancefrom said lower surface of said belt to the uppermost sheet which isbeing floated up by said air discharging portion.
 23. An image formingapparatus according to claim 19, wherein said controlling portion doesnot let said tray lifting and lowering portion lift and lower said traywhen the uppermost sheet is within said predetermined range.